Millimeter wave signals are used for radar and telecommunications. They are also capable of being used to generate data representative of a subject, by directing millimeter-wave signals at the subject and detecting the reflected signal. The data generated may then be used to produce an image of the subject. Examples of such imaging systems are described in U.S. Pat. Nos. 5,455,590; 5,557,283; 5,859,609; 6,507,309; and 6,703,964; U.S. patent application Ser. No. 10/607,552 filed Jun. 26, 2003; U.S. patent application Ser. No. 10/697,848 filed Oct. 30, 2003; and U.S. patent application Ser. No. 10/697,965 filed Oct. 30, 2003, which patent references are incorporated herein by reference.